MEMS technology is directed to the integration of mechanical elements, sensors, actuators, and electronics on a common substrate through the utilization of microfabrication technology. One such MEMS device is a MEMS switch. MEMS switches have the advantage of providing superior switching characteristics over a wide range of frequencies. One type of MEMS switch structure utilizes a cantilever beam design. A cantilever beam with contact metal thereon rests above an input signal line and an output signal line. During switch operation, the beam is electrostatically actuated by applying voltage to an electrode below the cantilever beam. Electrostatic force pulls the cantilever beam toward the input signal line and the output signal line, thus creating a conduction path between the input and output signal lines through the contact metal, also referred to as a shorting bar, on the cantilever beam.
A contact post is sometimes formed in each of the input and output signal lines. The contact posts form the portions of the signal lines that contact the shorting bar on the cantilever beam. Alternatively, the contact posts may be formed on the shorting bar. As such, the contact posts form the portions of the shorting bar that contact each of the signal lines. The shape, size, and height of the contact posts are important features of a MEMS switch because they define the contact area and how the switch makes contact with the shorting bar. That is, a contact post with sharp edges and protrusions at the perimeter can cause electrical arcing and degraded contacts thereby reducing the reliability of the MEMS switch. Consequently, the effective formation of contact posts is critical to MEMS switch fabrication and switch contact reliability.
The development of MEMS components is growing due to their low cost, small area, and high performance and reliability. One focus of attention has been directed toward a three-dimensional architecture of stacked substrates or wafers, with a MEMS device, such as a MEMS switch, located in a volume formed between the stacked substrates. The stacked substrates may additionally include integrated circuit device architecture along with the MEMS device thereby achieving further space savings, low cost, and high performance.
Challenges continue in the development of a more functional and cost-effective fabrication process for making MEMS switch contact posts that results in good contact post shape, size, and height control. In addition, the rising prominence of a three-dimensional architecture of stacked substrates necessitates a fabrication technique for making contact posts that is suitable for MEMS switch formation in the stacked configuration, and that achieves reliable mechanical and electrical contact characteristics.